The human heart has four valves; the aortic valve, the mitral valve, the pulmonary valve and the tricuspid valve. Various diseases and certain genetic defects of the heart valves can impair their proper functioning. The common defects and diseases affecting each of these valves, and the treatments thereof, are typically different.
As seen in FIGS. 1 and 2, the mitral valve is a two-leaflet (or bicuspid) structure of connective tissue separating the left atrium (LA) from the left ventricle (LV). The mitral valve functions to maintain blood flow in one direction, i.e., from the atrium toward the ventricle during ventricular relaxation or diastole, while preventing back flow in the opposite direction during ventricular contraction or systole. The bases of the two valve leaflets are attached to a circular fibrous structure of the heart called the annulus (AN), and their free edges to chordae tendinae arising from the papillary muscles of the left ventricle. An anterior leaflet (AL) is relatively large and attaches to the anterior segment of the annulus, while a posterior leaflet (PL) is smaller but extends further circumferentially and attaches to the posterior segment of the annulus. The posterior leaflet presents three scallops identified as P1, P2, P3, while the corresponding non-scalloped parts of the anterior leaflet are identified as A1, A2, and A3, according to Carpentier's segmentation.
Several diseases can affect the structure and function of the mitral valve. The mitral valve and, less frequently, the tricuspid valve, are prone to deformation and/or dilation of the valve annulus, tearing of the chordae tendineae and leaflet prolapse, which results in valvular insufficiency wherein the valve does not close properly and allows for regurgitation or back flow from the left ventricle into the left atrium. Deformations in the structure or shape of the mitral or tricuspid valve are repairable.
Mitral regurgitation is one of the most common valvular malfunctions in the adult population, and typically involves the elongation or dilation of the posterior two-thirds of the mitral valve annulus, the section corresponding to the posterior leaflet. The most common etiology of systolic mitral regurgitation is myxomatous degeneration, also termed mitral valve prolapse (29% to 70% of cases), which afflicts about 5 to 10 percent of the population in the U.S. Women are affected about twice as often as men. Myxomatous degeneration has been diagnosed as Barlow's syndrome, billowing or ballooning mitral valve, floppy mitral valve, floppy-valve syndrome, prolapsing mitral leaflet syndrome, or systolic click-murmur syndrome. The symptoms include palpitations, chest pain, syncope or dyspnea, and a mid-systolic click (with or without a late systolic murmur of mitral regurgitation). These latter symptoms are typically seen in patients with Barlow's syndrome, where extensive hooding and billowing of both leaflets are the rule. Some forms of mitral valve prolapse seem to be hereditary, though the condition has been associated with Marfan's syndrome, Grave's disease, and other disorders.
Myxomatous degeneration involves weakness in the leaflet structure, leading to thinning of the tissue and loss of coaptation. Barlow's disease is characterized by myxoid degeneration and appears early in life, often before the age of fifty. In Barlow's disease, one or both leaflets of the mitral valve protrude into the left atrium during the systolic phase of ventricular contraction. The valve leaflets are thick with considerable excess tissue, producing an undulating pattern at the free edges of the leaflets. The chordae are thickened, elongated and may be ruptured. Papillary muscles are occasionally elongated. The annulus is dilated and sometimes calcified. Some of these symptoms are present in other pathologies as well and, therefore, the present application will refer to myxoid degeneration, which is the common pathologic feature of the various diagnoses, including Barlow's syndrome.
Other causes of mitral regurgitation include ischemic heart disease with ischemic mitral regurgitation (IMR), dilated cardiomyopathy (in which the term “functional mitral regurgitation” [FMR] is used), rheumatic valve disease, mitral annular calcification, infective endocarditis, fibroelastic deficiency (FED), congenital anomalies, endocardial fibrosis, and collagen-vascular disorders. IMR is a specific subset of FMR, but both are usually associated with morphologically normal mitral leaflets. Thus, the types of valve disease that lead to regurgitation are varied and present vastly differently.
A number of these disease states have been schematically illustrated in FIGS. 4-8 with FIGS. 3A and 3B illustrating a normal mitral valve in plan and schematic sectional views across the anterior and posterior leaflets. FIGS. 4A and 4B show a mitral valve, also in plan and schematic sectional views, where the annulus is dilated and deformed causing mitral regurgitation. FIGS. 5A and 5B illustrate mitral valves with ruptured and elongated chordae, both causing mitral regurgitation. FIGS. 6A and 6B show symptoms of Barlow's disease with excess tissue and irregularly thickened leaflets. Barlow's disease is seen most often in the young population and has a long-lasting evolution before the onset of valve regurgitation. FIGS. 7A and 7B are views of a mitral valve having fibro-elastic deficiency with thinned leaflets and with excess tissue. Fibro-elastic deficiency, first described by Carpentier, is usually seen in more elderly people, and has a short-lasting evolution before valve regurgitation. The anatomical characteristics include a moderately enlarged kidney-shaped valvular orifice without excess leaflet tissue. The leaflet tissue displays a degeneration of the fibro-elastic bundles. Finally, FIGS. 8A and 8B illustrate the morphology of a mitral valve in Marfan's disease with excess and thin tissue and elongated chordae. Marfan's is a genetic disorder seen at any age. It has a long-lasting evolution before the onset of regurgitation. The annulus is severely dilated and deformed, the chordae are elongated, and the leaflets are thin and degenerative.
As is clear from the illustrations of FIGS. 4-8, many conditions lead to regurgitation. At a structural level, four general types of structural changes of the mitral valve apparatus can cause regurgitation: leaflet retraction from fibrosis and calcification, annular dilation, chordal abnormalities (including rupture, elongation, shortening, or apical tethering or “tenting” as seen in FMR and IMR), and possibly papillary muscle dysfunction.
Another approach to characterizing mitral valve disease is Carpentier's functional classification of the types of leaflet and chordal motion associated with mitral regurgitation. This is illustrated in FIGS. 9A-9D, which show anatomical positions during left ventricular systolic contraction when the leaflets of the mitral valve close or coapt. In Type I, FIG. 9A, excess dilatation of the annulus (seen in dashed outline) results in lack of coaptation between otherwise normal leaflets. Type II (seen in FIG. 9B) mitral regurgitation is due to leaflet prolapse or excessive motion because of rupture or elongation of the chordae tendinae. Type III involves restricted or tethered leaflet motion, classed as occurring during diastole Type IIIa (FIG. 9C) or during systole Type IIIb (FIG. 9D). Type IIIb (FIG. 9C) is typically seen in patients with ischemic mitral regurgitation. The course of the leaflets during the cardiac cycle is represented by the dotted lines. (Derived from Carpentier A: Cardiac valve surgery: the “French correction.” J Thorac Cardiovasc Surg 86: 323, 1983.)
Various surgical techniques may be used to repair diseased or damaged mitral and tricuspid valves. These include but are not limited to annuloplasty (i.e., contracting the valve annulus to restore the proper size and shape of the valve), quadrangular resection of the leaflets (i.e., removing tissue from enlarged or misshapen leaflets), commissurotomy (i.e., cutting the valve commissures to separate the valve leaflets), shortening and transposition of the chordae tendoneae, reattachment of severed chordae tendoneae or papillary muscle tissue, and decalcification of valve and annulus tissue.
In patients with degenerative mitral valve disease, valve repair using mitral valvuloplasty valve reconstruction, remodeling, or annuloplasty has been the standard for surgical correction of mitral regurgitation and has provided good long-term results. A rigid support ring (e.g., Carpentier-Edwards Classic® Annuloplasty Ring), a semi-flexible ring (e.g., Carpentier-Edwards Physio® Annuloplasty Ring), or a flexible curved band (e.g., Cosgrove-Edwards® Annuloplasty System) may be used. Closed rings are typically D- or kidney-shaped and generally exhibit a minor/major axis ratio of about 3:4. Some rings are flat or planar, while others exhibit three-dimensional bows. The rings are sutured to the deformed annulus so as to theoretically restore its normal shape and size and restore apposition of the leaflets. It should be noted that not all physicians agree which ring is appropriate for any one condition.
For illustration of conventional treatment, FIG. 10A is a surgeon's or plan view of a mitral valve having a deformed annulus leading to regurgitation. For decades, a suitable method of correcting such a deformed mitral valve annulus was to implant a prosthetic annuloplasty ring to restore normal apposition of the leaflets. FIG. 10B shows the annulus after implantation of a Carpentier-Edwards Physio® semi-flexible annuloplasty ring, the most frequently used ring in these cases, although a similar correction can be performed using other rings, such as those described in FIGS. 12-14. The aim of a conventional annuloplasty ring (and conventional wisdom) is to restore the shape of the normal mitral annulus, or, in some conditions, to overcorrect the shape by pulling inward a segment of the annulus. Unfortunately, the attachment of an annuloplasty ring sometimes leads to unintended consequences, as explained below
Despite accepted treatments for correcting mitral regurgitation, there is a need for a simpler and more effective approach that takes into account more of the common pathologies.